Abrasive articles are used in a variety of fields for abrading material from a surface of a workpiece. For example, an abrasive disc may be releasably mounted on a back-up pad for rotative movement by a random orbital sander. When the disc is rotated, and the exposed abrasive surface of the disc is urged against the workpiece surface, material may be removed from the workpiece. This operation may be desirable for surface refinement purposes, or for the removal of excess material from the workpiece.
Abrasive discs are typically releasably attached to a back-up pad, which supports the abrasive disc during the abrading process. Several types of abrasive discs have some type of attachment system incorporated into the disc to enable the disc to be releasably attached to a back-up pad. For example, abrasive discs having a layer of pressure sensitive adhesive ("PSA") on the back surface (the surface opposite the abrasive surface) are typically made by applying a layer of pressure sensitive adhesive on the back surface of the disc. One method used to produce these PSA abrasive discs is described in U.S. Pat. No. 3,849,949 (Steinhauser et al.), wherein adhesives such as vinyl ethers, acrylates, rubber resins, acrylic copolymers (such as a 95.5:4.5 isooctylacrylate:acrylic acid copolymer) are coated onto an abrasive sheet. The PSA is then dried or cooled, such that it is tacky but not flowable.
Although the foregoing process is useful, certain disadvantages are evident. For example, the PSA layer thickness (known in the processing field as the "coating weight") is often critical to the performance of the PSA abrasive disc, and precise control of the coating weight may be difficult to obtain by conventional coating methods. Furthermore, uniformity of PSA coating is also important to adhesion, and may be similarly difficult to obtain. Non-uniform PSA coating can lead to lack of adhesion (where PSA coating weight is reduced) or bumps in the surface of the abrasive disc (where PSA coating weight is increased). These potential disadvantages can be undesirable.
Another type of abrasive disc includes a textile material on the back surface of the disc. Abrasive discs of this type are disclosed in U.S. Pat. No. 4,437,269 (Shaw) and U.S. Pat. No. 4,609,581 (Ott), and an example of a textile abrasive disc is available from the Minnesota Mining and Manufacturing Company of St. Paul, Minn. under the designation Hookit.TM. discs. Textile discs are typically used in conjunction with a back-up pad having a plurality of engaging members that are bonded to the attachment surface of the back-up pad. The engaging members on the back-up pad are designed to engage the textile material of the textile disc, to secure the abrasive disc to the back-up pad.
The method of making a textile abrasive disc generally includes the steps of providing a loop material (such as a brushed nylon material available from Guilford Mills, Inc., of Greensboro, N.C. under the designation 33295), and laminating the loop material to an abrasive sheet using a suitable (for the textile or abrasive sheet member) water-based, solvent-based, or 100% solids hot-melt adhesive. The laminating adhesive is normally roll coated, sprayed, or extruded onto the abrasive sheet backing, and the loop material is then applied to the adhesive surface.
This method produces an acceptable abrasive disc, but certain disadvantages may again be evident. For example, suitable textiles are generally expensive, especially when compared to pressure sensitive adhesives. Also, the textile material often requires an added brushing step to provide a sufficient number of loops in an upright position to facilitate adequate attachment. Furthermore, the converting of textile-backed abrasive members to disc form requires unique equipment, such as high pressure presses and special handling apparatuses to collate the cut abrasive discs properly for packaging. Placement of the textile material onto the adhesive surface of an abrasive sheet may also be problematical, because the textile must be maintained in correct alignment with the adhesive-applied abrasive sheet member to prevent wrinkles in either the textile or abrasive sheet member.
The '269 patent referenced above also discloses a third type of abrasive disc. This type of disc, referred to herein as the "stalk disc," includes a plurality of engaging members in the form of inclined stalks. The stalks have unhooked ends, which slidingly intermesh with a textile material on a back-up pad to secure the abrasive disc to the back-up pad. The method used to make stalk discs generally involves a knitting process (such as warp knitting), that produces a woven base layer formed from multifilament yarn. Spaced stalks are woven into the knitted base layer, and are inclined with respect to, and project away from, the base layer. The woven stalk material may then be laminated to an abrasive sheet to produce an abrasive article.
Although stalk discs have some utility, the method used to produce such discs has certain disadvantages. The raw materials used to make stalk discs are more expensive than, for example, pressure sensitive adhesive materials. Other difficulties may arise during the converting process, such as damage to the stalks, lamination problems due to handling of the stalk fabric, and the like.
In view of the disadvantages associated with the various abrasive disc manufacturing methods of the prior art, it is desirable to provide a method of making an abrasive disc that overcomes those disadvantages.